1. Field of the Invention
The present invention relates to a slide positioner adapted to move any structural member from an inoperating position to a working or operating position.
2. Description of the Related Art
A slide positioner known from a brochure of G. C. Westec Ltd., Thunder Bay, Ontario, Canada, includes the various elements and features. A sliding shaft supporting a structural member (e.g., a so-called threading pan) has a polygonal (namely a square) cross section. A bearing device is adapted for supporting the sliding shaft and may be connected to a stationary frame. The bearing device is also connected to a linear motor, typically a pneumatic cylinder whose piston rod is connected to the sliding shaft. During the normal operation of the paper machine, the slide positioner holds the threading pan in a position beside the machine. During startup or after a web break, the threading pan is moved into an operating position and held there during the threading operation.
Additionally, the structural member to be moved may be a peeling or lifting nozzle (or separating blow pipe) which is used in a paper-making machine in order to peel off an edge strip (or xe2x80x9ctailxe2x80x9d) of the paper web produced, such as from a press roll or a drying cylinder. The structural member may also be a transfer device or a so-called mini-doctor which is used to transfer the edge strip to a following section of the paper machine. All those structural members are helpful to facilitate the threading of paper web into the machine when the machine is started up or after a web break.
Slide positioners of conventional design have proven successful in operation. However, a number of demands have prompted the need to improve the conventional design.
Those demands include the following objects:
A) Various mounting requirements, in particular on paper-making or paper-finishing machines, shall be met while maintaining the ability to accurately position the structural member in the machine in order to perform the desired task;
B) The manufacturing costs should be minimized by using interchangeable elements; and
C) Slide elements which are subject to wear due to friction between the sliding shaft and the bearing assemblies should be easily replaceable.
In one embodiment of the present invention, the sliding shaft includes two spaced bearing assemblies which are mountable relative to a stationary base in various angular positions. In other words, each bearing assembly is supported in a bore hole or in a circular cutout of the stationary base. As a result, the structural member supported by the sliding shaft can easily be brought into a convenient position (e.g., relative to the paper machine). Thereafter, the bearing assemblies are fixed to the stationary base, e.g., with bolts. Therefore, the slide positioner of the present invention, meets several different mounting requirements, e.g., on a paper-making machine, allowing the structural member to be accurately positioned in the place where it will operate.
In a preferred embodiment of the invention, the rotational axis of the bearing assemblies coincides with the axis of the sliding shaft. In other words, when the structural member is adjusted into its required angular position, the bearing assemblies together with the sliding shaft and with the linear motor are pivoted around the axis of the sliding shaft. Since the cylinder, specifically the stationary element of the linear motor, is connected to only one of the two bearing assemblies, the installation of linear motors of various stroke lengths is possible, without having to make any other changes to the slide positioner assembly.
According to another embodiment of the invention, the rotational axis of the bearing assemblies coincides with the axis of the linear motor. This design allows the mounting of the linear motor (e.g., pneumatic cylinder) directly onto the stationary base, so that the need for flexible pressure lines is avoided.
According to another aspect of the invention, each of the bearing assemblies includes at each surface of the polygonal sliding shaft a separate replaceable slide strip. Preferably, the sliding shaft has the form of a square tubing; in this case, each bearing assembly is fitted with four identical, replaceable slide strips. These are preferably manufactured from a self-lubricating material, e.g., PTFE (polytetraflouroethylene). This material reduces the friction forces between the sliding shaft and the bearing assemblies. If, nevertheless, one of the slide strips becomes worn, this single slide strip may be easily replaced, without having to disassemble the complete slide positioner.
It should be noted that the aforementioned separately replaceable slide strips may be use not only in the above-described bearing assemblies which are mountable to the base in various angular positions. Rather than that, the separately replaceable slide strips may also be used in conventional slide positioners having at least one rigidly mounted bearing device for the sliding shaft.